This invention relates to a new peroxy-carboxylic acid, to aqueous compositions containing percarboxylic acids and more specifically to their preparation and their use for disinfection.
Percarboxylic acids (peracids), by virtue of their properties, are contemplated for application in a wide range of uses, for example as oxidants, as stain removers and as microbicides, amongst others. The most well known prior art percarboxylic acid equilibrium solutions contain peracetic or perglutaric acid. The former is a very effective biocide, but it suffers from having an unpleasant odor, even in very dilute form. Perglutaric acid has no odor, but suffers from poorer biocidal properties than peracetic acid, especially at pH greater than 3, and on yeasts. Other odourless peracid solutions have been described based on a wide range of acids (i.e. citric, lactic, succinic, adipic acids etc), all of these peracids are either unstable in solution (i.e. lactic) or have limited biocidal properties.
As an alternative to compositions containing peracetic acid or perglutaric acid, WO 95/34537 and WO 98/28267 to Solvay Interox Limited reveal compositions based on ester peracids which have a low odor and effective biocidal properties, over a range of conditions.
It is an object of the present invention to provide a new peroxy-carboxylic acid. According to another aspect of the present invention there is provided to provide a new and effective process for preparing aqueous peracid compositions, without unpleasant odor and with good level of biocidal performance. Other objects of the present invention relate to the storage-stable aqueous peracid compositions and their use as a disinfectant.
According to the present invention there is provided a new percarboxylic acid compound, viz. compound of formula HOxe2x80x94(CH2)5xe2x80x94CO3H, which is also referred to in this text as 6-hydroxypercaproic acid.
In a further aspect, this invention provides a process for preparing aqueous percarboxylic acid compositions, which process comprises contacting a precursor of 6-hydroxypercaproic acid with a peroxygen compound.
In a particularly preferred embodiment, the precursor of 6-hydroxypercaproic acid is xcex5-caprolactone or water soluble dimers and/or oligomers thereof The special advantage of using xcex5-caprolactone is due to its high solubility in aqueous media.
In a further embodiment of the present invention, 6-hydroxypercaproic acid is obtained directly from 6-hydroxycaproic acid of formula HOxe2x80x94(CH2)5xe2x80x94COOH and/or from esters thereof.
During the contacting step, the precursor is preferably added in an amount up to about 30% by weight, generally from about 0.01% to about 20% by weight of the total weight of the reaction mixture containing the precursor, the peroxygen compound, water and the formed 6-hydroxy-percaproic acid.
The peroxygen compound used in this step may be any suitable organic or inorganic peroxygen compound capable of effecting the peroxidation of the precursor to 6-hydroxypercaproic acid. Hydrogen peroxide is particularly preferred as it avoids additional steps, such as neutralisation or partial neutralisation arising with alternative peroxygen compounds like sodium percarbonate or sodium perborate. The peroxygen compound is added in an amount up to about 30% by weight, generally from about 0.01% to about 20% by weight of the total weight of the reaction mixture as defined above.
The reaction between the precursor and the peroxygen compound, e. g. hydrogen peroxide, can be carried out in the absence of an acid catalyst. Alternatively, the reaction can be conducted in presence of a strong acid acting as a catalyst. This strong acid may be a mineral acid or an organic sulphonic acid, such as sulphuric acid, phosphoric acid and methanesulphonic acid, especially sulphuric acid. The acid catalyst is added in an amount of 0.1 to 5% by weight and often in an amount from 0.5 to 2% by weight of the total weight of the reaction mixture. By choosing the higher concentrations of acid catalyst it is possible to enable peroxidation to occur at a convenient rate without the need of elevated reaction temperatures.
The invention process can be carried out at temperatures within the range of from 10 to 50xc2x0 C. Use of a yet higher temperature tends to accelerate noticeably loss of available oxygen (Avox) from the compositions. In many instances the process is conducted at temperatures around ambient, i. e. between 15 and 30xc2x0 C., preferably at ambient temperature.
In another variation of the process, the contacting step is followed by an equilibrating step until the concentration of 6-hydroxypercaproic acid approaches its maximum or at least a substantial fraction thereof This can be achieved by monitoring the peracid content of the composition and the proportion of unreacted peroxygen compound, for example by periodic sample analysis.
As stated above, using a suitable concentration of acid catalyst within the range identified hereinbefore, the equilibrating step will take from less than 1 to about 10 days, depending on the nature of the precursor and of the peroxygen compound used to prepare the composition, as well as on the selected temperature. The equilibrating step may be conducted at a temperature within the same range as for the contacting step, preferably also at ambient temperature.
Optional components in the compositions according to the present invention comprise stabilisers and other additives such as catalysts, surfactants, chelating agents, corrosion inhibitors, thickeners, dyes, perfumes, scale removing agents such as mineral or organic acids and the like. The optional components can be present in a wide range of concentrations, but in many cases the total concentration of these components will not exceed 25% by weight of the total weight of the reaction mixture as defined above.
Stabilisers can desirably be employed to improve the storage stability of compositions according to the invention. Suitable stabilisers include hydroxy substituted aromatic carboxylic acids and ester derivatives thereof, particularly phenol carboxylic acids such as p-hydroxybenzoic acid and ester derivatives such as methyl or ethyl esters. They also include organic polyphosphonic acid sequestrants such as ethylidene diphosphonic acid, and aminopolymethylene-phosphonic acid, pyridine carboxylic acids, especially dipicolinic acid and mixtures thereof. In addition, inorganic stabilisers may be used. An example of inorganic stabiliser is colloidal tin. These compounds are often incorporated in an amount up to 5% by weight and generally in the range of from 0.025 to 1% by weight of the reaction mixture as defined above. When an acid stabiliser is used, it can also perform as catalyst.
In a further embodiment of the present invention there are provided aqueous percarboxylic acid compositions obtainable by a process of the invention.
In a further embodiment of the present invention there are provided aqueous percarboxylic acid compositions comprising 6-hydroxypercaproic acid and hydrogen peroxide.
Preferably, these compositions comprise up to 20% by weight 6-hydroxypercaproic acid, up to 20% by weight hydrogen peroxide and optionally up to 25% by weight total concentration of one or more stabilisers or other additives such as catalysts, surfactants, chelating agents, corrosion inhibitors, thickeners, dyes, perfumes, scale removing agents and the like.
The composition may be used as such or may be diluted by mixture with water. The extent of dilution is at the discretion of the process operator and depends on the intended use. It is often convenient to dilute until the solution has a peracid concentration in the region of about 0.0001 to 2% by weight. A composition containing such a concentration of peracid represents a ready to use disinfectant composition suitable in industrial and domestic disinfection applications.
The present invention concerns therefore also the use of the above described compositions as disinfectants. The method for disinfection according to the present invention comprises contacting the substrate to be disinfected with the composition. The composition may be employed with or without dilution. When compositions are diluted, dilution is usually chosen to give a 6-hydroxypercaproic acid concentration in solution of between about 1 part per million and 10000 parts per million, depending on the substrate. The disinfecting method can use a wide range of temperatures, typically from about 4xc2x0 C. to the boiling point of the disinfectant.
The composition of the invention can be used in a range of disinfection applications: e.g. disinfection of micro-organism contaminated aqueous media e.g. process waters containing bacteria, algae, yeasts and/or viruses from industries such as paper and pulp, food processing e.g. sugar refining, brewing, wine making, discharges from sewage treatment works, meat processing factories, carcase rendering and livestock rearing. Other substrates include irrigation water in the horticultural industry, contaminated cooling waters, and contaminated surfaces in e.g. food processing, horticulture, catering, domestic or hospital environments. The invention compositions can be used to treat crops and harvested plants or plant products.
It will nonetheless also be recognised that the peracid compositions according to the invention or produced by a process according to the invention may also be employed, if desired, for other purposes for which peracids are used, including bleaching or as a bleach additive in washing processes.